Embodiments of the present invention pertain to methods of pre-cleaning substrates in epitaxy chambers, systems, and apparatus. In particular, epitaxial deposition methods, systems, and apparatus that involve a cleaning process used to remove surface defects and contaminants prior to the epitaxy process are disclosed.
An epitaxial layer is a crystalline film grown over a crystalline substrate. The underlying substrate acts as a template for the growing film, so that the crystallographic characteristics of the epitaxial layer are defined by the underlying crystalline substrate. That is, the crystalline substrate provides a crystallographic seed for the epitaxial growth. The substrate may be, for example, monocrystalline silicon, silicon germanium, or an SOI wafer.
Growth of the epitaxial layer is commonly achieved using chemical vapor deposition (CVD). The substrate wafer is loaded into a CVD reactor, which is then purged with a non-reactive gas such as He, Ar, N2, or H2. The temperature of the reactor is ramped up, and a mixture of a carrier gas and a reactive gas is introduced into the reactor. Reactive gases may include, but are not limited to, silane (SiH4), disilane (Si2H6), trisilane (Si3H8), dichlorosilane (SiH2Cl2), trichlorosilane (SiHCl3), and silicon tetrachloride (SiCl4). Dopant gases may also be introduced, such as arsine (AsH3), phosphine (PH3) and diborane (B2H6). The carrier gas is typically hydrogen. When a desired thickness of the epitaxial layer has been achieved, non-reactive gases are again used to purge the reactor, and the temperature is ramped down.
However, for the epitaxial process to perform successfully, it is important that the amount of defects and contaminants present on the crystalline substrate be minimized. Crystallinity damage and contaminants on the crystalline substrate may arise during processing steps such as, for example, implantation, spacer etching, wet cleaning, and any other wafer fabrication step. The damaged and/or contaminated layer should be removed to avoid defects prior to the epitaxial deposition process. In one cleaning method, for example, the substrate may be annealed in a hydrogen atmosphere at a temperature in excess of about 850° C. to 1000° C., using what may be referred to in the art as a hydrogen pre-bake. However, such high temperature processes are expensive in terms of thermal budgeting. After the pre-bake step, the epitaxial deposition process may be performed.
It is desirable, therefore, to provide processes that reduce the thermal load during epitaxy. There is also a need for pre-clean processes that are performed at epitaxial growth conditions.